The present invention relates to a grinding wheel, particularly for deep grinding. More particularly, it relates to a grinding wheel which has a two-part grinding coating with one part composed of fine grain diamonds and another part formed on one side and containing coarse grain diamonds.
During deep grinding of a workpiece with a peripheral grinding wheel or with a cup grinding wheel with diamonds or cubic crystalline boron nitride, in the course of the service life of the grinding wheels a so-called roof profile is formed on the active surface of the grinding wheel. The form of the roof profile depends on the width of the grinding coating and the height of the adjustment of the grinding wheel. The main work of material removal is performed by a part of the grinding surface of the grinding wheel which is first as considered in the feeding direction, while the subsequent part determines the quality of the surface of the workpiece. Since different surface portions of the grinding wheel perform different tasks, it is known to design the part of the grinding surface differently with consideration of the different loads and more particularly to use in this portion different sizes of diamond grains as well as different concentrations of diamonds.
A known peripheral grinding wheel is provided on its peripheral surface and a known cup grinding wheel is provided on its end surface with fine grain diamonds which are held in a binder. The binder can be composed of for example of a phenol resin and copper. In the region of the grinding wheel which is subjected to higher loads the diamonds grains are arranged with greater classification, while in the region which determines the quality of the surface of workpiece diamonds of smaller specification are embedded. The regions have the binders of the same type, and the diamond grains are stochastically distributed in the binder in correspondence with respective volume fraction.
Conventionally the different coating zones are selected so that the grinding wheel with the coating part with fine grain specification can achieve the desired surface quality, while the coating part with the greater diamond grain specification does not break under the action of the loads at the predetermined material removal volume per time unit, and does not produce unpermissible forces and temperatures. It is recommended for a coating width of 5 mm, to provide such a distribution that the wider coating zone of 3 mm is provided for the fine grain part and a narrower coating zone of 2 mm is provided for the coarse grain part.
In the deep grinding in accordance with so-called quick-point process in which the axes between the grinding wheel and the workpiece are arranged in an inclined relation relative to one another, only an approximately point-shaped contact between grinding wheel and the workpiece is desired. The effective grinding wheel width must be selected as small as possible. Only then the object of the process to operate with very high material removal outputs can be achieved. As a result of this, a high loading of a small zone in the outer edge region of the grinding coating occurs. For preventing excessively high wear of the coating because of the high load, maximum coarse grinding grains in combination with a wear-resistant binder are to be selected. Only then the required true measurement on the workpiece can be obtained, since otherwise the wear of the grinding wheel causes shape deviations, especially cylindrical shape deviations in the workpiece.
On the other hand, by the selection of such a grinding coating, an excessively high roughness of the surface of the workpiece is produced. This is however not permissible for grinding. Thus the known constructions of the grinding wheels for this grinding process are not suitable for reaching the required surface roughness, or are characterized by excessively high wear or must be trued during the service life of the grinding wheels.